Fluorescent conjugated polymers have attracted much attention because of their potential optoelectronic and biological applications, such as light-emitting diodes, photovoltaic devices, field-effect transistors, nonlinear optics, and chemical and biological sensors. See, for example, A. J. Heeger, Angewandte Chemie, International Edition 2001, 40, 2591-2611. Among the conjugated polymers, polyfluorenes are being considered by many academic and industrial groups as a very promising blue light-emitting material due to their high photoluminescence quantum yield, high thermal and chemical stability, ease of emission color tuning, and facile modification at the 9-position of the fluorene ring without affecting main-chain conjugation. See, for example, U. Scherf and E. J. W. List, Advanced Materials (Weinheim, Germany) 2002, 14, 477-487.
Conjugated polymers containing aryl groups have been widely synthesized using various transition-metal-catalyzed or mediated step-growth polymerization techniques. These include Suzuli, Yamamoto, Haghihara/Sonogashira, and Kumada/GRIM techniques. The Suzuki technique is described in, for example, A. D. Schluter, Journal of Polymer Science, Part A: Polymer Chemistry 2001, 39, 1533-1556; and D. Marsitzlcy, R. Vestberg, P. Blainey, B. T. Tang, C. J. Hawker, and K. R. Carter, Journal of the American Chemical Society 2001, 123, 6965-6972. The Yamamoto technique is described in, for example, T. Yamamoto, Progress in Polymer Science 1992, 17, 1153-1205; and T. Yamamoto, A. Morita, Y. Miyazaki, T. Maruyama, H. Wakayama, Z. H. Zhou, Y. Nakamura, T. Kanbara, S. Sasaki, and K. Kubota, Macromolecules 1992, 25, 1214-1223. The Haghihara/Sonogashira technique is described in, for example, U. H. F. Bunz, Chemical Reviews (Washington, D.C.) 2000, 100, 1605-1644. And the Kumada/GRIM techniques are described, for example, in R. S. Loewe, P. C. Ewbank, J. Liu, L. Zhai, and R. D. McCullough, Macromolecules 2001, 34, 4324-4333; R. S. Loewe, S. M. Khersonsky, and R. D. McCullough, Advanced Materials (Weinheim, Germany) 1999, 11, 250-253; and U.S. Pat. No. 6,602,974 to McCullough et al.
Due to the synthetic requirement of specific coupling functionalities within the monomer units (boronic acid for Suzuki, terminal alkynes for Sonogashira, and activated halogens for Kumada/GRIM) the synthesis of these materials is often a challenge for chemists. To synthesize polyfluorenes, the Ni(0)-mediated Yamamoto-type polycondensation of dihalogenated fluorene has been preferred and widely used in the literature to produce homopolymers and copolymers prepared from fluorene and its 9-substituted derivatives. See, for example, Y.-H. Kim, Q. Zhao, and S.-K. Kwon, Journal of Polymer Science, Part A: Polymer Chemistry 2005, 44, 172-182; J. Cao, Q. Zhou, Y. Cheng, Y. Geng, L. Wang, D. Ma, X. Jing, and F. Wang, Synthetic Metals 2005, 152, 237-240; G. Zhou, G. Qian, L. Ma, Y. Cheng, Z. Xie, L. Wang, X. Jing, and F. Wang, Macromolecules 2005, 38, 5416-5424; R. Grisorio, P. Mastrorilli, C. F. Nobile, G. Romanazzi, G. P. Suranna, D. Acierno, and E. Amendola, Macromolecular Chemistry and Physics 2005, 206, 448-455; J. Lee, H.-J. Cho, B.-J. Jung, N. S. Cho, and H.-K. Shim, Macromolecules 2004, 37, 8523-8529; G. Tu, Q. Zhou, Y. Cheng, L. Wang, D. Ma, X. Jing, F. Wang, Applied Physics Letters 2004, 85, 2172-2174; X.-H. Zhou, J.-C. Yan, and J. Pei, Macromolecules 2004, 37, 7078-7080; L. D. Bozano, K. R. Carter, V. Y. Lee, R. D. Miller, R. DiPietro, and J. C. Scott, Journal of Applied Physics 2003, 94, 3061-3068; H.-J. Cho, B.-J. Jung, N. S. Cho, J. Lee, and H.-K. Shim, Macromolecules 2003, 36, 6704-6710; U. Asawapirom, and U. Scherf, Macromolecular Rapid Communications 2001, 22, 746-749; J.-I. Lee, G. Klaerner, and R. D. Miller, Chemistry of Materials 1999, 11, 1083-1088; G. Klaerner, and R. D. Miller, Macromolecules 1998, 31, 2007-2009; and Q. Pei and Y. Yang, Journal of the American Chemical Society 1996, 118, 7416-7417.
For the polymerization of dibromofluorenes, polymers with a very high number average molecular weight (Mn) of up to 200,000 g/mol have been reported. Microwave-assisted coupling procedure has been reported to increase the yield of the polymer and decrease the polymerization time significantly. See, for example, I(. R. Carter, Macromolecules 2002, 35, 6757-6759.
The Yamamoto polycondensation reaction involves the use of an equimolar amount of Ni(1,5-cyclooctadiene)2 (Ni(COD)2) as the coupling reagent with respect to the monomer. The advantages of Yamamoto polycondensation are that it can be used effectively along with various chemical functionalities to couple functional dihalogenated monomers giving polymers in good yields. But it is not a very convenient technique for polymerization since it requires large amounts of expensive catalyst (Ni(COD)2 equimolar to monomer), long reaction times, high reaction temperatures, inert atmosphere handling of Ni(COD)2, and the need for excess cyclooctadiene ligand, which is irritating and has an offensive smell.
There is therefore a desire for a polyfluorene synthesis method that avoids the use of cyclooctadiene ligand and uses a catalytic amount of coupling agent and reduced polymerization times and temperatures.